This invention concerns the automatic replenishment of chemical compositions consumed during photographic processes in which the compositions are used to develop photographic film.
In a photographic process, the latent image in exposed photosensitive emulsions is developed. In the course of the process, the compositions which chemically convert the latent image into a developed picture are consumed, and must be replaced. In black-and-white photography, the developer is consumed in reducing silver halide to metallic silver to create the image.
In color photography, the developer, such as CD-2 (a p-phenylenediamine derivative developer sold by Kodak), hydroquinone and the like, reduces the silver halide on the film to metallic silver, causing the color couplers to react to produce the colored dyes. Additionally, a bleach solution, such as sodium ferricyanide or the like, is used in oxidizing the metallic silver image to silver halide for subsequent solubilization in a fix solution, such as sodium or ammonium thiosulfate (Hypo) or the like, is used to dissolve the silver halide from the film. Other chemical solutions are also used in color photography processes, including stop (or short stop) baths, which are generally acidic solutions (typically acetic acid and the like, of a pH of 5.5 or less), are used instead of a rinse after development, and have the purpose of abruptly stopping development, hardner solutions (e.g. alkaline formalin), conditioner solutions, and the like.
If the photographic developing process is to proceed without interruption, it is necessary to make continuous measurements of the concentrations of the chemicals in the solutions and replenish the solutions with the depleted chemical in response thereto. Prior art photographic processing systems, however, have generally been constrained to replenish on a batch basis, or if continuous replenishment was performed it was done by making continuous measurements of the concentration of each chemical being consumed and replenishing the depleted chemicals on the basis of the measurements associated therewith. One such continuously operating system is disclosed in Schumacher U.S. Pat. No. 3,529,529 wherein the replenishment apparatus draws a sample of developer solution, performs a potentiometric titration to determine the concentration of halogen therein, and adjusts the flow rate of the developer replenisher in response thereto. This method is somewhat awkward and complicated in that titration solution must be stored and transferred, and the titration itself must be performed.
Other prior art systems as shown for instance in Hixon et al. U.S. Pat. No. 3,472,143 have replenished photographic chemicals in response to infrared sensing signals proportional to the area of film being processed. Still other systems as shown in Street et al. U.S. Pat. No. 3,554,109 have measured image density variations to control simultaneous replenishment of developer and fixer solutions. Other examples of prior art photographic replenishment systems are shown in U.S. Pat. Nos. 3,334,566 and 3,680,463.
All of these prior art systems, however, are considered to be awkward, inefficient, or impractical for commercial use in typical contemporary photographic processing laboratories. Further, most of the prior art systems applied to replenishment of single solutions used predominately in black and white film processing. Virtually no such work has been performed for color processing. Accordingly there has existed a need for an improved, simple, economical automatic process for replenishing the chemical compositions consumed during photographic processes.
Further, most processing laboratories are of a relatively small magnitude, and cannot afford to place a process controller on every process solution in the plant. A further need therefore exists for a method and means for controlling replenishment of the developing process chemicals without requiring individual process controllers of each solution.